This page has 2 parts:
Part 1 Dyno Chart Basics
& Part 2 Dyno Tuning Basics
Dynamometers are a tool, and like any tool
they can be used correctly or incorrectly.
Below is one of the more common ones:
This chart shows a ZX10R with a Sato slip-on, it is the same bike with no changes, EXCEPT the runs are done in different gears. Using 3rd, 4th, and 5th gears, it appears that the runs are different, but actually it is the scale that has made them appear different. Look at the bottom of the graph, it uses MPH instead or the more correct RPM. Since different gears were used the MPH is of course different, this moves the graph line for each run to the right or left. But the curves are the same as is the peak HP. The fact that different gears where used also shows up as each run ends at a different MPH, exactly what one would expect.
Below is the same three runs shown with the correct RPM used as the bottom scale. In this case what gear the bike was in does not matter as we are just reading RPM and HP.
see a set of runs and MPH is used on the bottom scale,
Below is a good example:
In this example two different gears were used, showing how much better their exhaust is, when in reality, it appears the stock system may have made more HP.
Dyno Tuning Basics
This next part started as a post I did on a forum, but I think it is relevant information & overlooked or misunderstood by many so I am going to display it permanently here
Dynojet has developed a way to interface their top of the line Dyno with their latest Powercommander products.
Now first & foremost the Powercommander basically only enhances what is already there based on the power delivery characteristics of the installed exhaust system. A good power curve from a quality exhaust will get better, but a bad power curve from a poorly designed exhaust is still going to be a poor curve even if it is improved upon. What we have seen time & time again is that good gains can be improved to a higher degree than poor gains can be improved. Exhaust dynamics is a tricky business, but if the flow is improved & the reversion waves are tuned properly then more fuel can be added & the more fuel you have the more power you get. If you have to remove fuel due to a poor flow design or the reversion waves are kicking back to the cylinder & meeting the next exhaust pulse at any point in the rev range then you simply are not going to get good power gains at that point. (that does not mean that a lean map is a bad one as sometimes the ECU's are just overich & the A/F has to be leaned out to become optimal)
The Dynojet 250 dyno is a Load Control dyno that basically makes the bike react as if it were on the road with a real rider on it by varying the load placed on the motor by using a huge electric brake that controls the force on the rotating dyno drum. By doing this it allows the tuner to determine the best possible Fuel mapping for not just full throttle, but for individual rpm & throttle position combinations (for example 5% throttle @ 4500 rpms) so you can tune for steady state cruise or roll-on acceleration as well as the typical full throttle run. Of course there are so many external variables involved inside the ECU's on todays current sportbikes, most of which revolve around passing EPA emissions testing, that it can be alot to compensate for when trying to get optimal performance out of your fuel injected bike. Just a side note: current technology can build engines that are so efficient they easily pass EPA emissions testing, what they have a hard time passing nowdays is the noise testing & yes the factories do alter the fueling in the ECU to help with the noise testing scenario too.
The majority of tuning all
comes down to the Air Fuel ratio. Optimum power is
generally around 12.6:1 while the stoichiometric value
for a gasoline burning engine is about 14.6:1 for a good
compromise of performance & mileage while Dynojet
themselves generally target 13.2:1 when they build their
own maps. The Dynojet 250 dyno has an O2 sensor as
standard equipment & the tuning link software used in
conjunction with a Powercommander (PCIIIr) can be set to
achieve a user specified Air/Fuel ratio target number
& the software will reprogram the Powercommander
automatically in a series of sampling stages. These
stages are set-up by the user and are basically
compromises from one to the next unless of course you set
the samples up identically.
Carburated bikes suffer
less from this as they don't have external variables from
the maps forcing them to change the mixture, but the dyno
results can still be skewed by not paying attention to
the outside variables during the run.
Some other things to note:
The PAIR valve system on all the new Honda's (& many other brands as well) injects fresh air into the headers. If you do not clamp off the tubes (or remove the entire PAIR system as many people do) before doing the dyno runs the exhaust gas analyzer will get false A/F readings of being overly rich.
Dyno testing in general can be very misleading & should only be used to show changes in power delivery on the same bike on the same dyno. Every dyno is different & will have different calibrations so you simply cannot compare dyno charts from two different dyno's & expect accurate results. In addition to the important & no so well known variables that I mentioned above such as the engine temp affecting the dyno results many other varaibles exist as well, Over-inflating your tires can yield higher numbers on the dyno and a well lubricated, properly adjusted chain will also insure better dyno results too...
I'll add more later as the need arises to cover more common questions & I get some typical feedback and/or questions about this page
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